# Analogue Pulse Counter Schematic

Posted on Mar 9, 2013

It was designed for an application in a welding machine: there are lots of bits of machinery which are cylindrical in shape and which are subjected to heavy surface wear. For instance ore crushers, and the idler and roller wheels off track laying vehicles, much used in earth moving. These wear quickly, so it makes sound economical sense to re-surface the component with a hard metal. This is typically done by a welding process, using a hard facing alloy.

As the item is rotated at a steady rate, the weld head oscillates fron side to side, laying down weld in a zig-zag or square wave pattern. At the end of a complete turn, the weld head is moved sideways by a distance more of less equal to the oscillation width, allowing for some overlap. On the last turn, the head must not be moved sideways but the weld must be 'over-run' a little to overlap into the new surface. Some machines are designed to handle components with a wide range of diameters. These machines used a stepper motor for the rotation, because they give such a wide range of speeds. This circuit is an analogue over-run counter for such a stepper rotator! As such an application, it is an uncommon requirement! But the circuit may be of general interest. This circuit is actually two main blocks, each of which may be useful in other ways. The first block, to the left, up to and including Tr5, is a cup-and-bucket charge pump. In case you don't know the term, it refers to a small capacitor (the cup - C1) dumping its charge into a larger one (the bucket). At a particular level, the bucket overflows and triggers something else. It's a sort of analogue divider if you will! The bucket is the 100n capacitor connected to the gate of the BF244 (J-FET). Input should be a pulse train (squarewave or similar) of repeatable amplitude fed into the count input. To start the circuit, Start input must go high enough to turn on...

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